Spectroscopy system

ABSTRACT

Systems and techniques for improved spectroscopy. In some embodiments, mechanical and/or optical zoom mechanisms may be provided for monochromator systems. For example, movable detector systems allow a detector to be positioned with respect to a dispersive element in order to obtain a first resolution. The detector systems may then allow the detector to be positioned with respect to a dispersive element to obtain a second different resolution. In some embodiments, spectroscopy of a first sample region may be performed using a plurality of excitation wavelengths. Multiple detectors may be positioned to receive light associated with different ones of the plurality of excitation wavelengths.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/268,148, which is hereby incorporated by reference in itsentirety.

BACKGROUND

1. Field of Invention

This invention generally relates to spectroscopy, particularly tomonochromator systems for spectroscopy (e.g., for Raman spectroscopy).

2. Related Art

A number of techniques may be used to obtain information aboutmaterials. One technique that may be used is Raman spectroscopy. InRaman spectroscopy, laser light is incident on a surface of a materialto be analyzed. Most of the light scatters elastically from the surface(which is referred to as Rayleigh scattering). However, some of thelight interacts with the material at and near the surface and isscattered inelastically due to excitation of vibrational, rotational,and/or other low-frequency modes of the material. The inelasticallyscattered light is shifted in wavelength with respect to the incidentlaser light, either down in frequency (corresponding to the excitationof a material mode by the incident photons, also referred to as RamanStokes), or up in frequency (corresponding to the interaction of theincident photons with an already-excited material mode, also referred toas an anti-Stokes Raman). The amount of the shift is independent of theexcitation wavelength, and the Stokes and anti-Stokes lines aredisplaced from the excitation signal by amounts of equal magnitude.

Raman spectroscopy is performed by detecting the wavelength-shiftedlight. In order to detect light of a particular wavelength of interest,such as Raman-shifted laser light, a spectroscopy system includes amonochromator.

FIG. 1 shows a simplified example of a Raman spectroscopy system 100,according to the prior art. A laser source 110 illuminates a sample 120mounted on a stage 130. Light 115 reflected from sample 120 includeselastically scattered light (which may be referred to as Rayleighscattered light), as well as inelastically (Raman) scattered light. Inorder to isolate the Raman scattered light, system 100 includes amonochromator 105, including a diffraction grating 140, a filteringmechanism such as a notch filter 155 and/or slit 107, and a fixeddetector 150. In order to analyze different regions of sample 120, stage130 may be used to provide relative movement of the sample with respectto the incoming light.

Light 115 is incident on a rotatable diffraction grating 140, whichdisperses the light according to its wavelength. In FIG. 1, the relativeposition of grating 140 and detector 150 is selected to detect a desiredwavelength λ_(d), but not to detect other wavelengths λ₁, λ₂, and λ₃.Because the Raman shift is relatively small, system 100 also includes anotch filter 155 positioned before detector 150 and configured to filterthe strong Rayleigh scattered component at the excitation wavelength.

Different detector types may be used. In older spectroscopy systems,photomultiplier tubes (PMTs) were common. However, PMTs integrate theoptical signal received on the entire detector surface. By contrast,newer spectroscopy systems generally use array detectors such as chargecoupled device (CCD) array detectors, complementary metal oxidesemiconductor (CMOS) detectors, and photodiode array detectors.

In order to detect the desired wavelength (and/or to scan a number ofwavelengths), some existing systems rotate diffraction grating 140,while detector 150 is fixed. For example, if wavelengths λ₁, λ₂, and λ₃are of interest, diffraction grating 140 may be rotated to scan therange of wavelengths shown in FIG. 1.

For existing spectroscopy systems, the wavelength resolution for aparticular measurement (i.e., the data collected at a particularrotation angle of diffraction grating 140) is fixed.

One way in which prior systems could be used to obtain more data aboutparticular wavelength ranges of interest was to scan the light acrossthe detector by rotating diffraction grating 140. For a low resolutionsystem, a user could first scan the wavelengths rapidly, by rotatingdiffraction grating 140 through a first angular range at a first speed.After identifying the wavelength ranges of interest, the user couldperform one or more additional scans. By performing the scans at aslower speed (and usually for a smaller angular range), the resolutionof the spectroscopy can be increased.

SUMMARY

In general, in one aspect, a spectroscopic system includes a dispersiveelement (such as a fixed or rotatable reflective diffraction grating,transmissive diffraction grating, prism, or other dispersive element)positioned to receive incoming light comprising a plurality ofwavelengths and to transmit wavelength-dispersed light. The systemfurther includes a detector configured to receive at least a portion ofthe wavelength-dispersed light, wherein the at least a portion of thedispersed light comprises divergent dispersed light. The system furtherincludes a moveable detector mount (such as a motorized rotation andlinear translation stage) configured to position the detector to receivea desired portion of the divergent dispersed light, and wherein thedetector is mounted to the moveable detector mount. The moveabledetector mount (e.g., motorized rotation and linear translation stage),may include a controller configured to receive signals indicative of adesired position of the detector, and to position the detector toreceive the desired portion of the divergent dispersed light at thedesired position.

The moveable detector mount may be configured to position the detectorat a pre-determined optical path length from the dispersive element toobtain a pre-determined resolution. The detector may be positioned at afirst pre-determined optical path length from the dispersive element toobtain a first resolution, and then positioned at a secondpre-determined optical path length from the dispersive element to obtaina second resolution. The second resolution may be higher than the firstresolution, and the second optical path length may be greater than thefirst optical path length.

The moveable detector mount may be configured to position the detectorat a first position having a first pre-determined angular relationshipto the dispersive element, and further configured to position thedetector at a second position having a second different pre-determinedangular relationship to the dispersive element.

The system may further be configured to perform depth profiling usinglight of different excitation wavelengths. For example, the plurality ofwavelengths may include a first excitation wavelength and a secondexcitation wavelength. The system may be configured to move the detectormount to a first position associated with the first excitationwavelength and to obtain spectroscopic data indicative of one or morephysical characteristics of a first sample region to a first depth. Thesystem may be configured to move the detector mount to a second positionassociated with the second excitation wavelength, and to obtainspectroscopic data indicative of the one or more physicalcharacteristics of the first sample region to a second different depth.The first position associated with the first excitation wavelength maycomprise a position to receive Raman shifted light from the first sampleregion, wherein the Raman shifted light comprises inelasticallyscattered light incident on the first sample region at the firstexcitation wavelength.

The plurality of wavelengths may include a first excitation wavelengthand a second excitation wavelength, and the system may further compriseanother detector configured to receive at least a portion of thedivergent dispersed light. The system may include another moveabledetector mount configured to position the another detector to receive adifferent desired portion of the divergent dispersed light. The anotherdetector may be mounted to the another moveable detector mount. Thedesired portion of the divergent dispersed light may comprise lightassociated with the first excitation wavelength, while the differentdesired portion of the divergent dispersed light may comprise lightassociated with the second excitation wavelength.

The dispersive element, the detector, and the moveable detector mountare included in a monochromator. The system may further comprise asample mount and a light source configured to generate light at a firstexcitation wavelength. The light source may be positioned to transmitlight at the first excitation wavelength to a sample mounted on thesample mount, and the dispersive element may be positioned to receivelight scattered from the sample in response to receiving the light atthe first excitation wavelength. The light scattered from the sample maycomprise Rayleigh scattered light and Raman scattered light.

The system may further comprise a light stopper adjacent to thedetector. The light stopper may be configured to allow light at a firstexcitation frequency to be received in the detector at a first time, andfurther configured to substantially prevent light at the firstexcitation frequency from being received in the detector at a seconddifferent time. The system may further comprise a movement mechanismconfigured to position the light stopper away from the detector at thefirst time.

The system may include one or more additional optical elements. Forexample, the system may further comprise a curved mirror positioned toreceive light reflected from a surface and to reflect the received lightas to the dispersive element as incoming light. The system may furthercomprise a second mirror, the second mirror configured to receivedispersed light from the dispersive element and to reflect the receiveddispersed light as divergent dispersed light.

In general, in another aspect, a monochromator system may include adispersive element configured to receive light including a plurality ofwavelengths and to disperse the plurality of wavelengths according towavelength. The system may further comprise a controller configured toreceive information indicative of a desired spectroscopic resolution andto generate one or more signals indicative of the desired spectroscopicresolution. The system may further comprise a zoom mechanism comprisingat least one of an optical zoom mechanism and a mechanical mechanism,wherein the zoom mechanism includes at least one element moveable withrespect to the dispersive element. The zoom mechanism may be incommunication with the controller and may be configured to move the atleast one element in response to receiving the one or more signalsindicative of the desired spectroscopic resolution.

For example, the zoom mechanism may comprise a mechanical zoom mechanismincluding a detector mount moveable with respect to the dispersiveelement. The detector mount may include a position controller configuredto receive the one or more signals indicative of the desiredspectroscopic resolution and to move the detector mount to a positionassociated with the desired spectroscopic resolution.

In another example, the zoom mechanism may comprise an optical zoommechanism including at least one moveable optical element, and whereinthe optical zoom mechanism is configured to receive the one or moresignals indicative of the desired spectroscopic resolution and to moveat least the one moveable optical element relative to the dispersiveelement to a position associated with the desired spectroscopicresolution. The monochromator system may include a detector configuredto receive Raman shifted light scattered from a sample.

In general, in another aspect, a monochromator system may comprise anoptical system configured to receive light scattered from a first regionof a sample surface in response to receiving light at a plurality ofexcitation wavelengths and to disperse the received light according towavelength. The system may further comprise a first detector mounted toa first moveable detector mount and a second detector mounted to asecond moveable detector mount. The first moveable detector mount may beconfigured to move the first detector to a first position associatedwith a first excitation wavelength of the plurality of excitationwavelengths. The second moveable detector mount may be configured tomove the second detector to a second position associated with a seconddifferent excitation wavelength of the plurality of excitationwavelengths.

The first detector may be further configured to detect a receivedportion of light scattered from the first region of the sample surfacein response to receiving light at the first excitation wavelength at afirst time, while the second detector may be further configured todetect a received portion of light scattered from the first region ofthe sample surface in response to receiving light at the secondexcitation wavelength at the first time.

The optical system may comprise a dispersion element selected from thegroup consisting of a transmissive diffraction grating, a reflectivetransmission grating, and a prism. The received portion of lightscattered from the first region of the sample surface in response toreceiving light at the first excitation wavelength at the first time mayinclude divergent light or substantially parallel light.

The first detector may further be configured to receive light scatteredfrom at least a second region of the sample surface in response toreceiving light at the first excitation wavelength at the first time.The optical system may include a first optical fiber positioned toreceive light scattered from the first region of the sample surface anda second optical fiber positioned to receive light scattered from thesecond region of the sample surface.

The first detector may comprise an array detector such as a detectorselected from the group consisting of a CCD array detector, a photodiodearray detector, and a CMOS detector. The optical system may include aflat mirror configured to reflect divergent light to be received in thefirst detector.

The light scattered from the first region of the sample surface inresponse to receiving light at the first excitation wavelength at thefirst time may be scattered from a portion of the first region of thesample surface extending downward a first depth, while the lightscattered from the first region of the sample surface in response toreceiving light at the second excitation wavelength at the first timemay be scattered from a portion of the first region of the samplesurface extending downward a second depth different than the firstdepth. The system may thus be configured to generate a depth profile ofthe sample.

In general, in another aspect, a spectroscopy method may includereceiving information indicative of a first desired resolution for aspectroscopy measurement. The method may further include positioning atleast a portion of a zoom apparatus relative to a dispersive elementbased on the first desired resolution. The method may further includeobtaining first spectroscopy data having the first desired resolutionwith the detector. The method may further include receiving informationindicative of a second desired resolution for a spectroscopy measurementand positioning the at least a portion of a zoom apparatus relative tothe dispersive element based on the second desired resolution. Themethod may further include obtaining second spectroscopy data having thesecond desired resolution with the detector.

The method may further include receiving information indicative of afirst desired wavelength range for the spectroscopy measurement, thefirst desired wavelength range extending from a first extremumwavelength (i.e., a minimum or maximum of the range) to a secondextremum wavelength (the other of the minimum or maximum of the range).The method may further include positioning the detector relative to thedispersive element based on the first extremum wavelength, and obtainingfirst spectroscopy data having the first desired resolution with thedetector may comprise scanning the detector relative to the dispersiveelement from the position based on the first extremum wavelength to aposition based on a second extremum wavelength.

The method may further include receiving information indicative of asecond desired wavelength range for the spectroscopy measurement, thesecond desired wavelength range extending from an initial extremumwavelength to a final associated extremum wavelength. The second desiredwavelength range may be smaller than the first desired wavelength range.The method may further include positioning the detector relative to thedispersive element based on the initial extremum wavelength. Thespectroscopy method may be a Raman spectroscopy method.

In general, in another aspect, a spectroscopy method may includegenerating excitation light comprising a plurality of substantiallydiscrete excitation wavelengths including a first excitation wavelengthand a second excitation wavelength. The method may further comprisescattering the excitation light from a first region of a sample anddispersing the scattered light according to wavelength. The method mayfurther comprise receiving a first portion of the dispersed light at afirst detector positioned to receive light associated with the firstexcitation wavelength and receiving a second different portion of thedispersed light at a second detector positioned to receive lightassociated with the second excitation wavelength. The method may furthercomprise determining one or more characteristics of the first region ofthe sample based on the first portion and the second portion.

Scattering the excitation light from a first region of a sample maycomprise scattering light having the first excitation wavelength from afirst depth of the first region of the sample, and may further comprisescattering light having the second excitation wavelength from a seconddifferent depth of the first region of the sample. The method mayfurther comprise determining one or more characteristics of the firstregion of the sample based on the first portion and the second portioncomprises generating a depth profile of the first region of the sample.The depth profile may comprise data indicative of one or more physicalcharacteristics of the first region of the sample at the first depth anddata indicative of one or more physical characteristics of the firstregion of the sample at the second depth.

These and other features and advantages of the present invention will bemore readily apparent from the detailed description of the exemplaryimplementations set forth below taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a Raman spectroscopy system, according to theprior art;

FIG. 2 is top view of a monochromator;

FIG. 3 is a schematic top view of a spectroscopy system, according tosome embodiments;

FIG. 4A is a top view of a monochromator system, according to someembodiments;

FIG. 4B illustrates the resolution differences for three differentradial positions of a detector in a spectroscopy system;

FIG. 4C is a perspective view of a monochromator system, according tosome embodiments;

FIG. 5 is a top view of an embodiment of a spectroscopy system;

FIG. 6 is a top view of an embodiment of a spectroscopy system to detectmultiple wavelengths;

FIG. 7 is a top view of another embodiment of a spectroscopy system todetect multiple wavelengths;

FIG. 8 is a top view of another embodiment of a spectroscopy system todetect multiple wavelengths;

FIGS. 9A and 9B are top views of embodiments of a spectroscopy system todetect multiple wavelengths;

FIG. 9C is a perspective view of an embodiment of a spectroscopy systemto detect multiple wavelengths;

FIG. 9D is an illustration of a CCD display for spectroscopy of multiplelocations of a sample;

FIG. 10 is a top view of an embodiment of a spectroscopy system showingboth equal distance and equal resolution configurations; and

FIG. 11 is a top view of an embodiment of a spectroscopy systemincorporating multiple lasers.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Systems and techniques provided herein may allow for more flexiblespectroscopy than provided by existing spectroscopy systems.

For optical spectrometers, monochromators are used to isolate particularwavelengths or wavelength ranges of interest. Typically, a user selectsa particular monochromator based on the anticipated application. Forexample, for Raman spectroscopy applications, bulky high resolutionmonochromators are generally used, to obtain high resolution data forthe Raman peaks of interest. For other applications, a user may wish tochoose a compact and easy to use low resolution monochromator.

In order to provide enhanced flexibility, systems and techniquesprovided herein include monochromator and spectrometer designs with zoomin/zoom out capability. As a result, both low and high resolutionspectroscopy may be performed.

FIG. 2 is a top view of a monochromator 205 illustrating the way inwhich the resolution of system 200 depends on the distance betweendiffraction grating 240 and detector 250, for divergent light incidenton detector 250.

When detector 250 is positioned at a distance d₁ that is relativelyclose to diffraction grating 240, it captures light from a relativelylarge solid angle. This provides a low resolution “view” of the material(i.e., a relatively large wavelength range of the reflected light).However, when detector 250 is positioned at a distance d₂ that isrelatively far from diffraction grating 240, it captures light from arelatively small solid angle. The captured light includes a narrowerwavelength range, providing a higher resolution view of the material.

FIG. 3 shows a diagram of a spectroscopy system 300 incorporating zoomin/zoom out capability, according to some embodiments. System 300includes a sample 320 mounted on a stage 330, and a monochromator system305. Monochromator system 305 includes a wavelength dispersion mechanismsuch as a diffraction grating 340 that is configured to disperseincluding light 315 according to wavelength. Monochromator 350 alsoincludes a movable detector 350. A user may control the position ofmovable detector 350 in order to obtain the desired spectral resolution.For example, the user may provide one or more parameters indicative of adesired positioning to the spectroscopy system via a user interface suchas a computer, and one or more controllers of system 300 (not shown) mayposition detector 350 based on the one or more parameters. In someembodiments, a user may position detector 350 at least partially usingone or more manual controls (e.g., knobs, levers, or other manualcontrol elements).

For example, at a first time t₁ detector 350 may be positioned at adistance d₁ from diffraction grating 340, and detector 350 may obtainlow resolution data of sample 320. The low resolution data may beanalyzed to determine one or more wavelength regions of interest. At alater time t₂, detector 350 may be positioned at a different distance d₁from diffraction grating 340, and detector 350 may obtain highresolution data of sample 320 (or of a different sample requiring higherresolution data).

Monochromator 305 may also be configured to provide relative angulardisplacement between diffraction grating 340 and detector 350. Therelative angular movement may be used to align detector 350 as desired(e.g., to capture Raman-shifted light) and/or to scan the beam acrossdetector 350. Relative angular motion may be provided by rotatingdetector 350 about diffraction grating 340, while diffraction grating340 is fixed. Instead (or in addition), diffraction grating 340 may berotated. Additionally, as noted above, dispersive elements other thanreflective diffraction gratings may be used, such as transmittancegratings or prisms.

Embodiments in which diffraction grating 340 is fixed may beparticularly beneficial for some applications. For example, in somespectroscopy systems, a number of additional optical elements (such asflat mirrors, curved mirrors, etc.) may be used with grating 340.Incorporating a moveable detector 350 may allow for enhanced ease ofuse. Rather than moving elements of the optical system to detect asignal at the wavelength of interest, the user need only calculate thedispersion angle of the wavelength of interest and/or determine thedesired resolution, and position detector 350 accordingly.

Detector 350 may be moved in a number of ways. For example, detector 350may be mounted on a stage 370 to provide the desired movement (e.g.,radial and/or angular movement). In some embodiments, stage 370 may be amotorized rotation and linear translation stage. The stage may include acontroller configured to receive signals indicative of a desiredposition of stage 370 and to move the stage in response to the receivedsignals.

System 300 may also include an inlet slit (not shown). Narrow inletslits may be used to improve the resolution, but may also reduce theamount of light that is available for detection. Larger inlet slitsincrease the amount of light available for detection, but the resolutionmay be less than desired.

FIG. 4A shows an embodiment of a monochromator system 405. System 405receives light (including light to be analyzed) through an input slit407 (which may have a width selected for the particular application, asnoted above). The light is reflected from a curved mirror 409 and isthen incident on a dispersive element such as a transmittance grating440. The dispersed light is reflected from a flat mirror 411. Differentportions of the reflected light may be received by a detector 450, whichmay be a CCD array detector, a photodiode array detector, complementarymetal oxide semiconductor (CMOS) detector, or other type of detector.

Note that some existing systems use a similar optical system to thatshown in FIG. 4A, except that instead of flat mirror 411, a curvedmirror is used. In those systems, the dispersed light reflects of thecurved mirror as parallel beams of light that differ in wavelengthacross their extent. By replacing the curved mirror with flat mirror411, the dispersed light diverges so that capturing the light atdifferent distances allows for measurements having different resolution.

FIG. 4B illustrates the different resolutions that may be obtained atthree different radial positions of detector 450. At a first positionclosest to mirror 411 (and thus with the shortest optical path length todiffraction grating 440), a low resolution spectrum may be obtained,containing a wide wavelength range. At a second position farthest frommirror 411, a high resolution spectrum, containing a narrow wavelengthrange, may be obtained. At a third, intermediate position, a mediumresolution spectrum may be obtained.

FIG. 4C is a perspective view of another embodiment of a monochromator405. Monochromator 405 includes an entrance slit 407 for receiving lightfrom a sample. The received light is incident on curved mirror 409, andthen dispersed by grating 440. In contrast to the monochromator of FIG.4A, flat mirror 411 is omitted. The dispersed light is incident on adetector 450, which may be positioned closer to grating 440 for lowerresolution or farther from grating 440 for higher resolution.

In some embodiments, optical zoom in/zoom out capability may be usedinstead of or in addition to the mechanical zoom in/zoom out capabilitydescribed above and illustrated in FIGS. 3, 4A, and 4C. For example, amonochromator may include a fixed detector, with one or more opticalelements positioned between the dispersion element and the detector. Theone or more optical elements may include a first fixed lens and a secondmoveable lens, so that the dispersion of the light is increased (zoomin, for increased resolution), or decreased (zoom out, for decreasedresolution) at the detector. In some embodiments, commercial zoomin/zoom out lens assemblies for camera systems may be used. However, forapplications in which the wavelengths used are unduly absorbed by glass,other lens materials may be needed. For example, quartz or other UVcompatible materials may be needed.

As noted above, in previous spectroscopy systems, a notch filter may beused to filter out the strong Rayleigh scattered laser signal, so thatthe Raman signal may be analyzed. However, for a system incorporating amoveable detector, such as the systems shown in FIGS. 3 and 4A anddescribed above, a different technique may be used, which may provideboth easier and more accurate spectroscopy calibration.

For Raman spectroscopy, the difference in wavelength between theexcitation wavelength λ_(exc) and the Raman wavelength λ_(Raman) may bedesignated as Δλ. In order to efficiently and accurately determineλ_(Raman), the Rayleigh scattered signal at λ_(exc) may be used tocalibrate the position of detector 550.

For example, detector 550 may initially be positioned at a distance fromdiffraction grating 540 so that both Rayleigh scattered light and Ramanscattered light can be captured across the breadth of detector 550(e.g., the resolution is low enough so that both signals may be detectedat the same time). Detector 550 may be moved angularly with respect tograting 540, until the strong Rayleigh scattered signal is detected andpositioned on detector 550 so that the Raman scattered light is alsocaptured by detector 550. Note that the relative positions of the Ramanand Rayleigh scattered light depend on whether the Stokes line, theanti-Stokes line, or both are to be detected.

Once detector 550 is positioned, a light stopper 552 may be moved intoposition by an actuator 554 (e.g., a micrometer), until the Rayleighscattered light is sufficiently blocked. The resulting Raman peak maythen be captured using detector 550. This may provide for more accuratespectroscopy, because the Raman peak is measured with respect to theposition of the detected Rayleigh peak, which serves as a wavelengthreference for the measurement.

The ability to rotate detector 550 angularly with respect to grating540, as illustrated in FIG. 5, may also be used to perform spectroscopyat multiple wavelengths. This may provide a significant benefit, sincedifferent wavelengths of light penetrate the sample to different depths.Larger wavelengths penetrate deeper into a material, while smallerwavelengths interact with the sample material closer to the samplesurface. As a result, using multiple wavelengths at the same time allowsfor a depth profile of the material to be obtained.

FIG. 6 shows a top view of a simplified spectrometry system 600 that maybe used to perform spectrometry at multiple wavelengths. A light source610 provides excitation light having more than one wavelength. Forexample, light source 610 may be a laser (such as an argon ion laser)that generates light at multiple excitation wavelengths, or may comprisemultiple lasers generating light at multiple wavelengths. In FIG. 6,signals with three wavelengths λ₁, λ₂, and λ₃, corresponding to threedifferent excitation wavelengths are dispersed by grating 640. In someembodiments, a single moveable detector 650 may be positioned angularlywith respect to a diffraction grating 640 to detect each of thewavelengths λ₁, λ₂, and λ₃ in turn. In other embodiments, threedifferent detectors 650, 650′, and 650″ may be positioned to detect eachof the wavelengths λ₁, λ₂, and λ₃ at the same time.

By contrast, in some existing systems, the diffraction grating isrotated so that the wavelength of interest is incident on a fixeddetector. In such systems, obtaining sample data at multiple wavelengthsmay be complicated. For example, a first set of sample data may beobtained at a first wavelength using a first light source. The lightsource may then be changed, and a second set of sample data obtained ata second wavelength. However, the system needs to be calibrated for thenew light source, and the second set of data correlated with the firstset. Thus, existing systems may be both more complex and less accuratethan using simultaneous excitation of the sample with multiplewavelengths.

FIG. 7 shows another implementation of a system 700, which may provide abetter signal to noise ratio for Raman scattered light. System 700includes a slit 722 so that specularly scattered light is not incidenton detectors 750, 750′, and 750.″ A collimated beam is incident ongrating 740, which disperses the light according to wavelength. FIG. 7illustrates and example where three wavelengths of interest are detectedin detectors 750, 750′, and 750″ (although of course different numbersof detectors may be used).

FIG. 8 shows another implementation of a system 800 for multiplewavelength excitation of a sample 820 mounted on a stage 830. Lightreflected from sample 820 may first be incident on one or more opticalelements 823, which may focus the light from sample 820 to betransmitted through a slit 822. The light may then be reflected from amirror 809 to a diffraction grating 840. The dispersed light may then bereflected from a flat mirror 800, and the wavelengths of interest maythen be detected in detectors 850, 850′, and 850.″ As with theimplementation of FIG. 4A, flat mirror 811 may be omitted in someembodiments.

FIGS. 9A to 9C show different implementations of systems that may beused to obtain depth profiling information using one or moremonochromators 905. For example, in FIG. 9A, light from one or morelasers 910 includes a plurality of excitation wavelengths (e.g., threedifferent wavelengths). The light is incident on sample 920, which ismounted on stage 930. Reflected light is incident on one or more opticalfibers 928, and transmitted to separate monochromators 905A, 905B, and905C, which have associated detectors 950, 950′, and 950.″

In FIG. 9B, light reflected from sample 920 on stage 930 is received ina fiber bundle 929 comprising a plurality of optical fibers. Thewavelengths of interest are then transmitted to separate monochromators905A, 905B, and 905C, or to a single monochromator 905 configured todetect multiple wavelengths.

In FIG. 9C, a larger area of sample 920 may be analyzed at a particulartime by incorporating a beam expander 913 after light source 910. Afiber bundle 929 may receive light from different regions of sample 920,and transmit the light to multiple monochromators, or to a singlemonochromator 905 having multiple associated detectors such as detectors950, 950′, and 955.″ A spectroscopy system such as that shown in FIG. 9Cmay be particularly useful for the semiconductor industry. When sample920 is a semiconductor sample such as a silicon wafer, different regionsof the wafer (e.g., 9 different regions corresponding to 9 fibers infiber bundle 929) may be analyzed at one time. FIG. 9D shows an exampleof a CCD output corresponding to simultaneous Raman spectrometry ofmultiple regions of the wafer. As FIG. 9D shows, detector pixelscorresponding to each of the sample regions shows a signal correspondingto the 520 cm⁻¹ Raman shift of silicon.

FIG. 10 shows an example of another spectroscopy system 1000 usingmultiple wavelength illumination of a sample 1010 positioned on a stage1005. Stage 1005 may be an X, Y, θ stage. A light source 1020 includes amulti-wavelength argon ion laser 1021, a diffraction grating 1022 (e.g.,a 1200 mm⁻¹ grating), and a collimating lens assembly 1023. Multiplewavelengths of light are incident on sample 1010 using optical fiberassembly 1050. Light from sample 1010, which may include reflected lightand Raman scattered light, is transmitted through optical fiber assembly1050 to a slit assembly 1052. In the illustrated embodiment, differentfibers of assembly 1050 transmit light of different wavelengths tosample 1010, while one fiber transmits light from sample 1010 to slitassembly 1052.

The light is reflected using a curved focusing mirror 1054, thendifferent wavelengths are dispersed using a dispersion element such as adiffraction grating 1056 (e.g., a 1200 mm⁻¹ grating). Divergent lightfrom grating 1056 is received by detectors 1058A, 1058B, and 1058C.

The systems and techniques described herein may be configured in anumber of ways. For example, FIG. 10 illustrates two different detectorconfigurations that may be used, for particular applications. In anequal resolution configuration, detectors 1058A, 1058B, and 1058C arepositioned at a distance from diffraction grating 1056 so that theresolution obtained is the same for the different wavelengths. In anequal distance configuration, detectors 1058A, 1058B, and 1058C arepositioned at an equal distance from diffraction grating 1056.

FIG. 11 shows an embodiment of a system 1100 incorporating differentlasers to generate different wavelengths. A first argon ion laser 1121Agenerates light having a wavelength of 457.9 nm, while a second argonion laser 1121B generates light having a wavelength of 488.0 nm, and athird argon ion laser 1121C generates light having a wavelength of 514.5nm. The light is reflected to a diffraction grating 1122 (e.g., a 1200mm⁻¹ grating) using optical elements 1126A, 1126B, and 1126C, which maybe mirrors or diffraction gratings. As above, the light is thencollimated in a collimating lens assembly 1123.

Multiple wavelengths of light are incident on sample 1110 mounted onstage 1105, using optical fiber assembly 1150. Light from sample 1110,which may include reflected light and Raman scattered light, istransmitted through optical fiber assembly 1150 to a slit assembly 1152.In the illustrated embodiment, different fibers of assembly 1150transmit light of different wavelengths to sample 1110, while one fibertransmits light from sample 1110 to slit assembly 1152.

The light is reflected using a curved focusing mirror 1154, thendifferent wavelengths are dispersed using a dispersion element such as adiffraction grating 1156 (e.g., a 1200 mm⁻¹ grating). Divergent lightfrom grating 1156 is received by detectors 1158A, 1158B, and 1158C. FIG.11 illustrates both an equal distance and an equal resolutionconfiguration for the detectors.

The actual system used may be tailored for the particular spectroscopyapplication. For example, for a Raman spectroscopy system, a system withfixed optical elements may be desired because of its reliability.However, for other spectroscopy applications (e.g., photoluminescenceapplications), the range of wave numbers to be detected may be largeenough that rotation of the dispersion element may be desired.

Similarly, in some applications a dispersion element may be used withoutother optical elements (or with just a slit or similar mechanism).Although such a system may receive more scattered light at the detector,the magnitude of the desired signal may be larger, since there is noattenuation due to the interaction of the light with additional opticalelements such as mirrors and lenses. However, in some applicationsadditional optical elements may provide a better signal to noise ration,despite the additional attenuation.

In implementations, the above described techniques and their variationsmay be implemented at least partially as computer software instructions.Such instructions may be stored on one or more machine-readable storagemedia or devices and are executed by, e.g., one or more computerprocessors, or cause the machine, to perform the described functions andoperations.

A number of implementations have been described. Although only a fewimplementations have been disclosed in detail above, other modificationsare possible, and this disclosure is intended to cover all suchmodifications, and most particularly, any modification which might bepredictable to a person having ordinary skill in the art. For example,many types of optical elements may be used in the monochromator andspectroscopy system.

Also, only those claims which use the word “means” are intended to beinterpreted under 35 USC 112, sixth paragraph. Moreover, no limitationsfrom the specification are intended to be read into any claims, unlessthose limitations are expressly included in the claims. Accordingly,other embodiments are within the scope of the following claims.

1. A monochromator system, comprising: an optical system configured toreceive light scattered from a first region of a sample surface inresponse to receiving light at a plurality of excitation wavelengths andto disperse the received light according to wavelength; a first detectormounted to a first moveable detector mount; a second detector mounted toa second moveable detector mount; wherein the first moveable detectormount is configured to move the first detector to a first positionassociated with a first excitation wavelength of the plurality ofexcitation wavelengths, and wherein the second moveable detector mountis configured to move the second detector to a second positionassociated with a second different excitation wavelength of theplurality of excitation wavelengths; and wherein the first detector isfurther configured to detect a received portion of light scattered fromthe first region of the sample surface in response to receiving light atthe first excitation wavelength at a first time, and wherein the seconddetector is further configured to detect a received portion of lightscattered from the first region of the sample surface in response toreceiving light at the second excitation wavelength at the first time.2. The system of claim 1, wherein the optical system comprises adispersion element selected from the group consisting of a transmissivediffraction grating, a reflective transmission grating, and a prism. 3.The system of claim 2, wherein the received portion of light scatteredfrom the first region of the sample surface in response to receivinglight at the first excitation wavelength at the first time includesdivergent light.
 4. The system of claim 3, wherein the received portionof light scattered from the first region of the sample surface inresponse to receiving light at the first excitation wavelength at thefirst time includes substantially parallel light.
 5. The system of claim2, wherein the first detector is further configured to receive lightscattered from at least a second region of the sample surface inresponse to receiving light at the first excitation wavelength at thefirst time.
 6. The system of claim 5, wherein the optical systemincludes a first optical fiber positioned to receive light scatteredfrom the first region of the sample surface and a second optical fiberpositioned to receive light scattered from the second region of thesample surface.
 7. The system of claim 1, wherein the first detectorcomprises a detector selected from the group consisting of a CCD arraydetector, a photodiode array detector, and a CMOS detector.
 8. Thesystem of claim 1, wherein the optical system includes a flat mirrorconfigured to reflect divergent light to be received in the firstdetector.
 9. The system of claim 1, wherein the light scattered from thefirst region of the sample surface in response to receiving light at thefirst excitation wavelength at the first time is scattered from aportion of the first region of the sample surface extending downward afirst depth, and wherein the light scattered from the first region ofthe sample surface in response to receiving light at the secondexcitation wavelength at the first time is scattered from a portion ofthe first region of the sample surface extending downward a second depthdifferent than the first depth.
 10. A spectroscopy method comprising:generating excitation light comprising a plurality of substantiallydiscrete excitation wavelengths including a first excitation wavelengthand a second excitation wavelength; scattering the excitation light froma first region of a sample; dispersing the scattered light according towavelength; receiving a first portion of the dispersed light at a firstdetector positioned to receive light associated with the firstexcitation wavelength; receiving a second different portion of thedispersed light at a second detector positioned to receive lightassociated with the second excitation wavelength; and determining one ormore characteristics of the first region of the sample based on thefirst portion and the second portion.
 11. The method of claim 10,wherein the scattering the excitation light from a first region of asample comprises scattering light having the first excitation wavelengthfrom a first depth of the first region of the sample, and furthercomprises scattering light having the second excitation wavelength froma second different depth of the first region of the sample.
 12. Themethod of claim 11, wherein determining one or more characteristics ofthe first region of the sample based on the first portion and the secondportion comprises generating a depth profile of the first region of thesample.
 13. The method of claim 12, wherein the depth profile comprisesdata indicative of one or more physical characteristics of the firstregion of the sample at the first depth and data indicative of one ormore physical characteristics of the first region of the sample at thesecond depth.
 14. The method of claim 10, further comprising: prior toreceiving the first portion of the dispersed light at a first detectorpositioned to receive light associated with the first excitationwavelength and receiving the second different portion of the dispersedlight at a second detector positioned to receive light associated withthe second excitation wavelength, positioning the first detector and thesecond detector at a substantially equal distance from a disperser. 15.The method of claim 10, further comprising: prior to receiving the firstportion of the dispersed light at a first detector positioned to receivelight associated with the first excitation wavelength and receiving thesecond different portion of the dispersed light at a second detectorpositioned to receive light associated with the second excitationwavelength, positioning the first detector and the second detector atdifferent distances from a disperser, the different distances selectedto provide a substantially equal resolution.